Firmness in processed vegetables and fruits

ABSTRACT

Firmness of processed canned foods including fruits and vegetables has been markedly improved by subjecting the fruit or vegetable to a low temperature blanching step at a temperature in the range of 125° F. to 160° F. and preferably from about 140° F. to 155° F. prior to conventional sterilization. Determination of blanch temperature conditions to produce optimum firmness in the processed food is made by first obtaining firmness values of specific foods at various blanch and hold temperatures and thereafter plotting the rate of firmness increase (Newtons/minute) against blanch temperatures. Preferred conditions, which vary for different foods, are obtained from individual plots for each food. Synergistic improvement of firmness results by combining the low temperature blanching with food grade acid (pH) and/or calcium salt additions.

This is a divisional of copending Ser. No. 08/262,353, filed Jun. 20,1994, which is a continuation of Ser. No. 08/135,575, filed Oct. 13,1993, now abandoned, which is continuation of Ser. No. 08/022,433, filedFeb. 16, 1993, now abandoned, which is a continuation of Ser. No.07/540,399, filed Jun. 19, 1990, now abandoned, which is a continuationof Ser. No. 07/279,907, filed Dec. 5 1988, now abandoned.

The present invention relates to improved methods of food processing.More specifically it relates to improving the firmness of fruits andvegetables which are processed by blanching followed by sterilization.

BACKGROUND OF THE INVENTION

Thermal processing is one of the most important methods mankind hasdeveloped for extending the storage life of perishable foodstuffs.However, the thermal process causes some destruction of the foodqualities. Nutritional value, texture, color and flavor are usuallydamaged to a greater or lesser extent during the thermal process.

The soft texture of most canned vegetables is recognized as a majorquality defect. It is probably one of the main reasons why the sales ofcanned vegetables are declining while sales of fresh vegetables areincreasing. Protecting food against excessive softening caused bythermal processing is an on-going problem.

VanBuren et al, J. Food Sci., 27:291 (1962), have processed snap beansusing a low temperature blanch at about 170° F. before canning to give afirmer-textured canned snap bean as compared to the conventionalblanching at 200° to 212° F. The vegetable canning industry typicallyuses a blanch temperature of about 170° F. for snap beans. Similarly,Lee et al, J. Food Sci., 44:615 (1979) have shown that a 170° F. blanchgives firmer textured canned carrots.

Large quantities of vegetables and fruits are preserved by canning. Thistechnology requires enclosing the product in hermetically sealedcontainers and heating at a specified temperature for a specified timeto destroy all microorganisms inside the container. Products with a pHabove 4.5 require a substantial heating regime to obtain commercialsterility. For example, green beans packed in brine in 1 lb cans require22 minutes at 240° F. or 13 minutes at 250° F. This heavy heat treatmentcannot be compromised because microorganisms of public healthsignificance, such as Clostridium botulinum, require this degree of heattreatment to be destroyed. Unfortunately, this amount of heat causesgreat damage to the food texture. Most canned vegetables have a softerthan desirable texture.

The present invention relates to a process for improving fruit andvegetable firmness, particularly in thermal processed foods.

BRIEF DESCRIPTION OF THE INVENTION

One object of the present invention is to improve the firmness of cannedfruits and vegetables subjected to thermal sterilization processing bypredetermining optimum low-temperature blanch temperatures for each foodfrom softening curves and a plot of the rate of firmness increase withblanch temperature.

Another object is to provide a process to prepare canned fruits andvegetables having improved firmness qualities by using lower blanchtemperatures and optimum holding times prior to sterilization to replaceor as an adjunct to conventional processing methods.

Another object is to maximize the factors that contribute to foodfirmness by selecting conditions for increasing the firmness andsimultaneously countering conditions which have the effect of softeningthe food.

Yet another object relates to a low temperature blanching process formaintaining the firmness of fruits and vegetables subjected tosterilization processing which comprises blanching the fruits orvegetables at a temperature of from about 125° F. to about 160° F. priorto sterilization for a time sufficient to cause said fruit or vegetableto remain firmer after sterilization as compared to said fruit orvegetable sterilized without said blanching step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a softening curve graph of log extrusion force (KN) versusprocess time in minutes for diced beets processed at 220° F.

FIG. 2 is a softening point curve where firmness (N) is plotted againstprocessing time in minutes for cut green beans in #303 cans, blanched at3 minutes at 74° C. (165.2° F.); the National Food Processor recommendsa process time of 22 minutes at this temperature.

FIG. 3 is a graph comparing a softening curve for Nantes carrot blanched4 minutes at 74° C. and 100° C. respectively before processing at 100°C.

FIG. 4 is a series of graphs for Nantes carrots processed at 250° F.where the log of the firmness is plotted against process time in minutestogether with equations for lines of best fit and correlationcoefficient R, data used to measure substrate "b" and thermal firmnessvalue (y-axis intersect).

FIG. 5 is a plot of the thermal firmness versus hold time (minutes)after 3 minutes blanching at various temperatures where the slope oflines equal the rate of firmness increase.

FIG. 6 is a plot of the rate of firmness increase (Newtons per minute)vs. blanch temperature (degrees Fahrenheit) for Chantenay var. carrots.From the graph, optimum blanch temperatures can be selected based onrates of firmness increase.

FIG. 7 is a graph of rate of firmness increase versus blanch temperaturefor three varities of green beans, namely Labrador, Bonanza and BBL 47.

FIG. 8 is a graph of rate of firmness increase versus blanch temperaturefor three varieties of carrots, namely Nantes, Danvers and Chantenay.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to improved methods of food processing andparticularly relates to improving the firmness of fruits and vegetablesover commercial processes requiring a blanching step followed bysterilization.

The invention relates to a process to increase or maintain the firmnessof fruits and vegetables subjected to thermal sterilization processingwhich comprises;

a) preparing a fruit or vegetable for sterilization processing;

b) blanching the fruit or vegetable at a temperature in the range offrom about 125° F. to about 160° F., preferably from 135° F. to 155° F.and most preferably at temperatures from about 140° F. to about 150° F.;wherein the optimum blanching temperature is determined in advance forthe fruit or vegetable as follows:

(1) determining the thermal firmness of the said fruit or vegetable as afunction of the blanching temperature and blanch time;

(2) determining the rate of thermal firmness increase with blanch timefor a series of blanching temperatures;

(3) selecting blanch temperatures or ranges thereof based on (1) and (2)adapted to provide an optimum firmness increase.

c) holding the blanched fruit or vegetable for a hold period of time upto 120 minutes before sterilization processing;

d) sterilizing the product resulting from step (c).

The thermal firmness and the rate of increase of thermal firmness withblanch temperatures and blanch time can be determined by variousmethods. A preferred method is to determine the firmness of the fruit orvegetable as a function of the blanching temperature and blanch time anddetermine the thermal firmness therefrom. By plotting the thermalfirmness versus blanch time for a series of blanching temperatures, onedetermines the rate of thermal firmness increase. When the rate ofthermal firmness increase is graphed against blanch temperature a curveis obtained which allows one to conveniently select a blanch temperatureadapted to provide an optimum firmness increase.

Another aspect of the invention relates to a method for furtherenhancing the firmness of fruits or vegetables subjected to thermalprocessing by combining the above process with treatments usingfood-grade multivalent salt compounds such as for example magnesiumchloride, magnesium oxide, magnesium sulfate, calcium chloride, calciumsulphate, calcium oxide, calcium acetate, calcium citrate and the like;food grade acids selected from the group consisting of citric acid,acetic acid, malic acid, tartaric acid, lactic acid and the like orcombinations of both.

It is recognized that the invention can be practiced using a variety ofblanch temperature and times preceding further processing stepsincluding thermal sterilization. Thus blanch time as used herein isdefined broadly as the time the product is held at the blanchtemperature and includes a holding time where the blanched product isheld for a defined period prior to sterilization processing.

Another aspect of the invention relates to the use of a low blanchingtemperature sufficient to activate the natural enzyme which promotesfirmness in said fruit or vegetable but lower than the temperature whichinactivates such enzyme.

DISCUSSION

Kinetic studies have shown that the rates of thermal softening ofthermally processed fruits and vegetables is a two-phase process. Thereis an initial rapid rate of softening which is followed by a much slowerrate of softening.

Huang and Bourne (J. Texture Studies, 10:1-23 (1983)) investigated theeffect of thermal processing on the firmness of vegetables. Theseauthors measured firmness by placing the sample in a back extrusion cellmounted in the Instron Universal testing machine (cf. Bourne and Moyer1968). The back extrusion cell used was 10.2 cm I.D. by 12 cm heightwith a 4 mm annulus. Extrusion speed was 30 cm/min and the downwardmovement of the plunger was reversed 6 mm from the bottom of the cell.The maximum peak of the recorded force-distance curve, measured inKilonewtons, was taken as the firmness of the commodity.

The effect of process time on firmness of fruits and vegetables can beshown by plotting log extrusion force vs. process time. Typicalsoftening curves are shown in FIGS. 1, 2 and 3. The softening curve ischaracterized by an initial rapid decrease in firmness (negative slope)that is almost linear but which curves off into a second straight linewith a shallow negative slope at longer process times. Since afirst-order kinetic process is represented by a rectilinear plot on asemilogarithmic scale it is evident that simple first-order kineticsdoes not apply when lengthy process times are used on canned vegetables.The general shape of this curve is typical for all vegetables studied.Fruits show similar thermal softening curves but the initial rate ofsoftening is completed more rapidly than for vegetables.

The shape of these experimental curves is similar to that obtained forthe sum of two independent simultaneous first-order processes occurringat different rates. From analogy with kinetic theory the linear portionof the semi-logarithmic curve that is obtained after prolonged heatingtimes (referred to as mechanism 2) gives the apparent softening rateconstant for this mechanism. When the linear portion of mechanism 2 isextrapolated back to zero process time and the extrapolated linesubtracted from the line above it, the result is a second straight linewith a much steeper slope (referred to as mechanism 1) and the slope ofthis derived line gives the apparent softening rate constant formechanism 1. This kinetic evidence indicates that the softening ofvegetables during thermal processing is composed of two pseudofirst-order processes with different rate constants occurringsimultaneously. One process is rapid and the other process is slow.

From analogy with kinetic theory for two apparent first order processeswe can postulate that the firmness of vegetable tissue is composed oftwo substrates, "a" and "b" and that substrate "a" softens rapidly bymechanism 1 while substrate "b" softens slowly by a different mechanism(mechanism 2). When the linear portion of mechanism 2 is extrapolatedback to zero process time (dotted line in FIG. 1) and this extrapolatedline is subtracted from the solid line above it, a second line isobtained as shown by the open circles and dashed line in FIG. 1. Thederived dashed line represents mechanism 1 and the slope is its apparentrate constant. The linear portion of the solid line represents mechanism2 and the slope is its apparent rate constant.

Predicting Process Conditions for Optimum Firmness

As shown in the best mode examples (Table 1, FIG. 6), a plot of the rateof firmness increase (Newtons per minute) versus blanch temperaturegives a graph which allows one to select blanch temperatures to produceoptimum firmness in the shortest time.

For example, with reference to FIG. 6, suitable blanch temperatureranges for Chantenay variety of carrots can be selected directly fromthe graph. Broad ranges are those falling within rate of firmnessincrease (Newtons/minute) of up to about 1.5, i.e. temperatures of 125°F. to 170° F.; preferred ranges are those with rate of firmness increaseof 1.50 or greater (i.e. temperatures of from about 135°-155° F.) andmost preferred ranges are those having positive rate increase of 2.5-3.0(i.e. temperatures of from about 140° to about 150° F.).

It is recognized that because of the differences in the food types to beprocessed, the temperatures and the holding times sufficient to producethe described rate of firmness increase will vary. Generally the bestblanching temperature will be broadly in the range of about 120° F. to160° F. sufficient to provide a fast rate of firmness increase inNewton's/minute; preferably at about 135° F. to about 155° F.; and mostpreferably at a temperature from about 140° to about 150° C. sufficientto provide the fastest rate of firmness rate increase. It is recommendedthat experiments be run to establish graphs for each food type to beprocessed.

A wide variety of vegetables can be processed according to the presentinvention. These include for example, carrots, beets, potatoes, waxbeans, green beans, cauliflower and the like.

Similarly the invention is applicable to a wide variety of fruits suchas peaches, apples, cherries, pears and the like.

The following best mode examples are meant to illustrate the invention;they should not be narrowly constructed as to limit the invention.

EXAMPLE 1

Two carrot varieties (Nantes and Chantenay) were washed, topped, dicedinto 3/8" cubes on an Urschel dicing machine and small pieces removed bypassing over a shaking screen. Seven 5 Kg lots of diced carrot wereweighed for each blanch temperature. Nine blanch temperatures wereused--120°, 130°, 140°, 150°, 160°, 170°, 180°, 190°, 200° F. Each lotwas blanched 6 min. in water at the designated temperature, then removedfrom the water and held with no further heating for a designated holdtime, then blanched again 3 minutes at 212° F. in water to stop furtherenzyme activity and cooled by immersion in cold water. Hold temperatureswere 0, 15, 30, 45, 60, 75, 90 minutes.

Sixteen #303 cans were filled from each of the 63 blanchtemperature-hold time combinations (7 hold times×9 blanch temperatures).One 60 grain salt tablet was added to each can. The cans were filledwith near boiling water, closed, and processed at 250° F. in steam instill retorts with pressure cooling at the conclusion of the designatedprocess time. For each blanch temperature-hold time: 4 cans wereprocessed 40 minutes; 4 cans were processed 60 minutes; 4 cans wereprocessed 80 minutes; 4 cans were processed 100 minutes.

Beginning one week later, the cans were opened and the firmness measuredusing a back extrusion cell (7.4 cm I.D.×7.8 cm internal height with a 4mm wide annulus) mounted in an Instron Universal testing machine. Thismachine plots on a strip chart the force required to extrude thevegetable up through the 4 mm wide annulus between the descending ramand the inside wall of back extrusion cell. This test was replicatedeight times for each sample. The maximum force was measured from theInstron chart and the mean value calculated for each treatment.

The logarithm of the mean firmness was graphed against the process timein minutes. A typical series of graphs so obtained is shown in FIG. 4which gives the data for the 140° F. blanch treatment of Chantenaycarrots. The calculated line of best fit to the data points is drawn.The intercept of this line on the vertical axis (firmness at zeroprocess time) is called "thermal firmness".

The thermal firmness data are then graphed against hold time afterblanch and the calculated time of best fit is drawn. A typical graph isshown in FIG. 5 for each of 9 blanch temperatures for Chantenay carrot.The slope of each line is measured and this is the rate of increase inthermal firmness for each blanch temperature (shown at the right handedge of the figure).

The data obtained from FIG. 5 is then graphed against blanch temperatureto give FIG. 6. This figure shows that the rate of increase of thermalfirmness increases as the blanch temperature rises from 120° F. to 150°F. and then decreases at temperatures above 150° F. In this case, forChantenay carrot, 150° F. blanch gives the fastest rate of increase inthermal firmness.

Food processors prefer to keep holding times as short as possible.Graphs like FIG. 6 enable processors to determine a blanchtemperature-hold time regime that will give a firmer textured product inthe shortest possible time.

Table 1 shows thermal firmness values versus hold times in minutes forChantenay and Nantes variety carrots.

                  TABLE 1                                                         ______________________________________                                        Thermal Firmness (Force (N)) Versus Hold Time*                                ______________________________________                                        Chantenay Carrots                                                             Hold Time                                                                              Blanch Temperatures (°F.)                                     (minutes)                                                                              120    130      140  150    160  170                                 ______________________________________                                         0       199.5  195.0    245.5                                                                              239.9  251.2                                                                              223.9                               15       182.0  234.4    346.7                                                                              363.1  269.2                                                                              234.4                               30       218.8  316.2    371.5                                                                              436.5  263.0                                                                              218.8                               45       234.4  316.2    501.2                                                                              467.7  302.0                                                                              245.5                               60       213.8  323.6    501.2                                                                              457.1  346.7                                                                              245.5                               75       229.1  309.0    467.7                                                                              524.8  371.5                                                                              229.1                               90       281.8  331.1    489.8                                                                              549.5  389.0                                                                              234.4                               ______________________________________                                        Chantenay Carrots                                                             Hold Time  Blanch Temperatures (°F.)                                   (minutes)  180           190    200                                           ______________________________________                                         0         213.8         204.2  218.8                                         15         213.8         204.2  195.0                                         30         223.9         213.8  213.8                                         45         234.4         229.1  223.9                                         60         218.8         234.4  199.5                                         75         229.1         199.5  204.2                                         90         218.8         199.5  195.0                                         ______________________________________                                        Nantes Carrots                                                                Hold Time                                                                              Blanch Temperatures (°F.)                                     (minutes)                                                                              120    130      140  150    160  170                                 ______________________________________                                         0       169.8  195.0    169.8                                                                              204.2  269.2                                                                              245.5                               15       269.1  208.9    239.9                                                                              309.0  302.0                                                                              263.0                               30       275.4  218.7    269.2                                                                              346.7  363.1                                                                              263.0                               45       281.8  295.1    316.2                                                                              380.2  398.1                                                                              257.0                               60       338.8  295.1    363.1                                                                              446.7  380.2                                                                              302.0                               75       309.0  309.0    338.8                                                                              457.1  436.5                                                                              263.0                               90       426.6  380.2    398.1                                                                              467.7  426.6                                                                              218.8                               ______________________________________                                        Nantes Carrots                                                                Hold Time  Blanch Temperatures (°F.)                                   (minutes)  180           190    200                                           ______________________________________                                         0         223.9         173.8  166.0                                         15         186.2         169.8  173.8                                         30         213.8         182.0  169.8                                         45         229.1         166.0  154.9                                         60         204.2         166.0  169.8                                         75         213.8         182.0  162.2                                         90         223.9         173.8  162.2                                         ______________________________________                                         *Time Interval Minutes between end of blanch and beginning of thermal         sterilization.                                                           

Table 1 shows that a conventional process of a 200° F. blanch (no holdtime) give thermal firmness values of 219N and 166N respectively forChantenay and Nantes variety carrots with no increase of firmness forholding times of 30 minutes after blanching. However, when the carrotsare blanched at 150° F. the respective thermal firmness values are 240Nand 204N and these increase to 437N and 346N at 30 minutes hold and to550N and 460N at 90 minutes hold time. Thus a low temperature blanchtemperature plus hold time before sterilization gives a marked increasein firmness. FIG. 5 shows a plot of thermal firmness versus hold time(minutes) for Chantenay carrots. It is seen that firmness increases mostrapidly for 150° F. and 140° F. blanched carrots, less rapidly for 130°and 160° blanch. There is only slight increase of thermal firmness withhold time for the remaining blanch temperatures.

FIG. 6 is a graph of rate of firmness increase (newtons/minute) versusblanch temperature for Chantenay carrots. Both FIGS. 5 and 6 allow oneto select optimum blanch temperatures and hold times for optimumfirmness.

Referring to FIG. 6 it is seen that desirable blanch temperatures forChantenay carrot are broadly from about 125° F. to about 160° F.,preferably from about 135° to 155° F. and most preferably from about140° to about 150° F.

EXAMPLE 2

In an experiment similar to that of Example 1, Danvers variety ofcarrots was evaluated using 4° F. increments in blanch temperatures overthe range of 140° to 160° F. to more critically define this range. Theresults are shown in Table 2 and FIG. 8.

                  TABLE 2                                                         ______________________________________                                        Firmness of Canned Danvers Carrot (Newtons Force)                             Hold Time                                                                              Blanch Temperatures (°F.)                                     (minutes)                                                                              140    144      148  152    156  160                                 ______________________________________                                         0       247.6  206.0    191.0                                                                              234.9  259.2                                                                              254.3                               15       294.6  333.3    303.2                                                                              339.0  337.5                                                                              264.7                               30       364.6  327.2    376.5                                                                              368.2  359.5                                                                              270.7                               45       452.7  444.6    393.7                                                                              402.1  394.7                                                                              287.4                               60       513.7  452.6    413.0                                                                              405.7  352.7                                                                              299.6                               75       424.1  449.4    400.5                                                                              432.4  372.2                                                                              293.3                               90       449.1  474.2    437.3                                                                              393.2  364.5                                                                              304.1                               ______________________________________                                    

From the above it is seen that the 144° F. blanch temperature gave thefastest rate of increase in firmness; however, temperatures of 140°,148° and 152° F. also gave high values for the rate of firmnessincrease. FIG. 8 also shows a rate of firmness increase for two othercarrot varieties (Nantes, Chantenay) in the narrower blanch temperaturerange of 140° F. to 160° F.

EXAMPLE 3

Ten Kg lots of Danvers variety carrots (unpeeled) were blanched 15minutes and 30 minutes at 150° F. They were then peeled, sliced anddiced and sterilized for 24 minutes at 250° F. in #303 cans (21 cans pertreatment). For comparison purposes a control was blanched 4 minutes at212° F. with no hold time before peeling, cutting and sterilization. Thefirmness results (newton's) are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Firmness of Canned Carrot (in Newton's Force)                                 Treatment                                                                     Blanch Temp. °F.                                                                         Type   Firmness (N) & SD                                    ______________________________________                                         4 min. at 212° F. (control)                                                             slices 214 N ± 11.7                                      15 min. at 150° F.                                                                       slices 255 N ± 10.7                                      30 min. at 150° F.                                                                       slices 328 N ± 14.9                                       8 min. at 212° F.                                                                       dices  202 N ± 8.1                                       15 min. at 150° F.                                                                       dices  268 N ± 10.9                                      30 min. at 150° F.                                                                       dices  317 N ± 15.3                                      ______________________________________                                    

From Table 3, it is seen that a 150° F. blanch for 15 and 30 minutesgives a marked increase in firmness as compared with conventionalprocessing of 212° F. for 4 minutes.

EXAMPLE 4

In an experiment similar to Example 1, three varieties of snap beanswere processed to establish the blanch temperature that gives thefastest rate of increase of thermal firmness. The varieties wereLabrador (a green bean), BBL-47 (a green bean) and Bonanza (a wax bean).Example 1 protocol was used except for the following differences:

1) the beans were cut into 11/2 inch lengths;

2) hold times of 0, 15, 30, 45 and 60 minutes were used;

3) blanch temperatures were 120°, 130°, 140°, 145°, 150°, 160°, 170° and180° F.

The results are shown graphically in FIG. 7 which is a graph of the rateof firmness increase versus blanch temperature. The difference in themaximum rate of firmness increase is noted i.e. 130° F. for Bonanza;145° F. for BBL-47 and 150° F. for Labrador.

EXAMPLE 5

Heads of cauliflower were broken apart into curds, then blanched 10minutes at 145° F. in hot water containing 6 grams of citric acid perliter, hold for 20 minutes, then sterilized in No. 303 cans for 22minutes at 240° F. As a control some of the curds were blanched 4minutes at 200°-210° F. then sterilized in the same manner with no holdtime. The mean value of 8 replicate texture measurements showed that thefirmness (newton's force) for the 145° F. blanched product was 127 asopposed to 65 for the control.

EXAMPLE 6

Small white potatoes (B grade) were peeled in an abrasive rotary peelingmachine, then blanched 15 or 30 minutes at 145° F., filled into No. 303cans and sterilized 26 minutes at 250° F. in a still retort. A controlbatch of potatoes was sterilized at 250° F. for 26 minutes withoutblanching. The blanched potatoes gave a mean firmness values of 405 and431N as opposed to 378N for the control.

EXAMPLE 7

Two types of sweet cherries (Sodus-light variety and Duron II--a darkvariety) were blanched 5 minutes at 140° F., then held for 30, 60, 120minutes before being canned in 20 percent sugar syrup and sterilized at212° F. for 20 minutes. For controls, some cherries were canned with noblanch treatment which is the conventional commercial procedure.Firmness was measured as the force in newtons to push Dunkley cherrypitters simultaneously through 30 cherries. The firmness is shown inTable 3.

    ______________________________________                                        Treatment,  Hold Time Firmness  (Newtons Force)                               Blanch Temp, °F.                                                                   (minutes) Sodus     Durone II                                     ______________________________________                                        Control (no blanch)                                                                       --         87        97                                           140° F.                                                                            30        116       114                                           140° F.                                                                            60        114       146                                           140° F.                                                                            120       128       164                                           ______________________________________                                    

Normally, cherries are not blanched but processed in syrup. It is seenthat low temperature blanch (140° F.) with 30, 60 and 120 minutes holdtimes gives increased firmness.

EXAMPLE 8

Freestone peaches were cut in halves and blanched 20 minutes in waterheld at 145°-150° F., held for 2 hours and then canned in 25 percentsugar syrup using a sterilization of 20 minutes at 212° F. Controlpeaches were canned with no blanch treatment which representsconventional commercial practice. Firmness was measured in a backextrusion cell. Four days later another lot of the same peaches wereblanched 30 minutes and canned immediately with no hold time beforesterilization. The peaches blanched 20 minutes at 145° F. with a 2 hourhold gave a firmness (newton's force) of 221, while those blanched 30minutes at 145° F. with no hold gave a firmness of 237. Both resultsexceeded the control firmness of 174N.

EXAMPLE 9

Golden Delicious apples were blanched 30 minutes (9A) and 60 minutes(9B) at 145° F. in water, then peeled, sliced and canned in 20 percentsugar syrup with a sterilization of 20 minutes at 212° F. Control appleswere canned with no blanch which is the conventional process. Firmnesswas measured in the back extrusion cell. The firmness in newton's force,223 for sample 9A and 265 for 9B, greatly exceeded the control of 89.

EXAMPLE 10

It is well known in the food processing industry that the addition ofcompounds such as salts of calcium or magnesium impart firmer texture toprocessed vegetables and fruits. Two vegetables (green beans andpotatoes) and one fruit (peaches) were canned with and without 0.07percent added calcium chloride after being subjected to a conventionalcommercial blanch or a blanch in the 140°-150° F. range as described inthe prior art examples. Firmness results using a back extrusion cell aregiven in the following table:

                  TABLE 5                                                         ______________________________________                                                              Hold     Firmness                                                Blanch       Time     Without                                                                              With                                    Product  Temperature  (minutes)                                                                              Calcium                                                                              Calcium                                 ______________________________________                                        Green beans                                                                            205° F.                                                                             --       218    266                                     (BBL-47) 145° F.                                                                             30       476    646                                     Potatoes no blanch    (control)                                                                              378    362                                     (white)  145° F.                                                                             15       405    402                                              145° F.                                                                             30       431    407                                     Peaches  no blanch    (control)                                                                              174    221                                     (Freestone)                                                                            20 min. @ 145° F.                                                                   120      221    269                                              30 min. @ 145° F.                                                                    0       237    289                                     ______________________________________                                    

The results in Table 5 above, show that a firmer product is produced inboth green beans and peaches using either a 145° F. or a calciumtreatment. A synergistic effect is noted for the combined treatmentusing both 145° F. blanch and calcium salt. Note the firmness of greenbeans increases to 646 with calcium and blanch versus 476 (blanch alone)as compared with 266 (calcium only) and 218 (no calcium), for the 205°F. blanch control. These limited tests showed no synergism for potatoes.

EXAMPLE 11

It is known in the food industry that the heating regime needed tosterilize foods with a pH below about 4.5 is much less rigorous than forfoods with a pH above 4.5 because heat resistant bacterial spores cannotgrow below pH 4.5. This example is to show the effect of the combinationof a milder heat sterilization with the addition of sufficient acid tobring the pH of a food having a pH higher than 4.5 to a pH of below 4.5.

Carrots, green beans and cauliflower were given a conventionalcommercial blanch treatment, or a blanch in the 145°-150° range beforeprocessing with, and without, calcium and sufficient acid to reduce thepH below 4.5. The products without the addition of acid were given acommercial high temperature sterilization. The products with added acidwere sterilized for 20 minutes at 212° F. which is sufficient to obtaincommercial Sterility because the pH was below 4.5. The results are shownin Table 6.

Dramatic synergism is noted for carrots, green beans and cauliflower.For carrots an 8 minute blanch at 212° F. followed by sterilizationusing both calcium and citric acid gives a firmness of 2168 newton'sforce. In contrast, a blanch at 150° F. for 15 or 30 minutes using bothcalcium and citric acid gives firmness values of 3058 and 3485 newton'sforce. The combination of calcium plus citric acid and 145° F. blanchand 20 min. (212° F.) sterilization gives a 2168 firmness forcauliflower and 4376 for green beans.

                  TABLE 6                                                         ______________________________________                                        Effect of Added Calcium and Acid on Firmness                                  ______________________________________                                        Treatment                                                                     Product Blanch        Sterilization                                           ______________________________________                                        carrots,                                                                              8 min. at 212° F.                                                                    24 min. at 250° F., still retort                 Danvers 8 min. at 212° F.                                                                    --                                                      sliced  8 min. at 212° F.                                                                    20 min. at 212° F., still retort                         15 min. at 150° F.                                                                   24 min. at 250° F., still retort                         --            --                                                              --            20 min. at 212° F., still retort                         30 min. at 150° F.                                                                   24 min. at 250° F., still retort                         --            --                                                              --            20 min. at 212° F.                               green beans                                                                           6 min. at 172° F.                                                                    8.5 min. at 250° F. in Steritort                 RBL-47  4 min. at 145° F.                                                                    --                                                              (hold 30 min.)                                                                --            20 min. at 212° F., still retort                 cauliflower                                                                           6 min. at 212° F.                                                                    22 min. at 240° F., still retort                         10 min. at 145° F.                                                                   --                                                              (hold 30 min.)                                                                --            20 min. at 212° F. in water                      ______________________________________                                               Treatment                                                              Product  Additives      Firmness - Newtons Force                              ______________________________________                                        carrots, none           202                                                   Danvers  +Ca            279                                                   sliced   +Ca + citric acid                                                                            2168                                                           none           268                                                            +Ca            362                                                            +Ca + citric acid                                                                            3058                                                           none           317                                                            +Ca            440                                                            +Ca + citric acid                                                                            3485                                                  green beans                                                                            none           336                                                   RBL-47   none           454                                                            +Ca + vinegar  4376                                                  cauliflower                                                                            none            65                                                            none           127                                                            +Ca + citric acid                                                                            2168                                                  ______________________________________                                    

What is claimed is:
 1. A process for producing canned fruits andvegetables which are subjected to sterilization after canning, whichprocess comprises, before canning, blanching a fruit or vegetabledifferent from green beans, wax beans and cauliflower at a temperatureof from about 125° F. to 155° F. for a time sufficient to cause saidfruit or vegetable to remain firmer after sterilization as compared tosaid same fruit or vegetable after canning and subsequent sterilizationwithout said blanching step.
 2. A process of claim 1 wherein theblanching temperature is from about 140° F. to about 150° F.
 3. Theprocess of claim 1 wherein the blanching temperature is from about 140°to 150° F., food grade calcium salt and food grade acid are added to thefruit or vegetable prior to sterilization, the food grade calcium saltis calcium chloride and the food grade acid is selected from the groupconsisting of acetic acid, citric acid, lactic acid, malic acid,tartaric acid and mixtures thereof.
 4. The process of claim 1 whereinthe fruit or vegetable is potatoes.
 5. The process of claim 1 whereinthe fruit or vegetable is peaches.
 6. The process of claim 1 wherein thefruit or vegetable is apples.
 7. A process for producing canned fruitsor vegetables which are subjected to sterilization after canning, whichprocess comprises, before canning, blanching a fruit or vegetable at atemperature of from about 125° F. to 155° F. for a time sufficient tocause said fruit or vegetable to remain firmer after sterilization ascompared to said same fruit or vegetable after canning and subsequentsterilization without said blanching step and enhancing the firmness ofthe sterilized fruit or vegetable by adding a food grade acid to thefruit or vegetable prior to the sterilization to reduce pH below 4.5.